The invention relates to an intraocular lens.
Such an intraocular lens is disclosed in U.S. Pat. No. 5,217,491. The known intraocular lens consists of a foldable optical lens part made of a soft, especially swellable material, as for example pHEMA (polyhydroxyethyl methacrylate) or a copolymer thereof, and a harder haptic part of PMMA (polymethyl methacrylate). In this disclosure it is furthermore stated that the experiment was undertaken to produce a lens blank in which the core forming the optical lens part is formed from a HEMA-MMA copolymer and a harder ring surrounding the latter for the later haptic of PMMA. In the case of a pHEMA/MMA ratio of 75:25, the core could be pressed out from a disc-shaped blank. With a pHEMA/MMA ratio of 50:50 the core was tight in the outer ring, but the core separated from the PMMA ring after hydration in water.
In a further test a lens blank was produced in which the core intended for the optical lens part was prepared from a HEMA-MMA copolymer with a HEMA/MMA ratio of 75:25 with a harder haptic ring of PMMA with small HEMA percentages in an MMA/HEMA ratio in the starting solution of 90:20 and 80:20. For the lens blank with a pHEMA/MMA ratio of 75:25, a tight bond was formed between the haptic ring and the optical core. The latter lens blank did not have, however, sufficiently lasting hydrolysis stability. This is also the case with the lens blank in which the core is made by the polymerization of HEMA and TEGDMA as crosslinker, the core is then swollen and then a PMMA ring is formed around the core using EGDMA as crosslinker.
EP 0 269 288 A1 discloses the use of a copolymer of 80 g HEMA and 20 g MMA as material for an intraocular lens. It is also known from this disclosure to add EDGMA to a copolymer in a ratio of admixture of 65:35.
DE 38 00 529 A1 has disclosed a copolymer of 85% HEMA and 15% MMA crosslinked with 0.5% EDGMA for the production of an intraocular lens. What is involved is copolymers of a low degree of crosslinkage.
U.S. Pat. No. 4,871,785 discloses primarily copolymers containing HEMA for the production of contact lenses, which are also said to be suitable for intraocular lenses, and in which a high percentage of crosslinking agent is used.
Particularly in the biological environment of the eye no long-term resistance to hydrolysis is obtained. This is due mainly to the fact that the aqueous humor and enzymes present therein have a hydrolyzing effect on the lens material, especially the optical part thereof.
The invention is addressed to the problem of creating an intraocular lens of the kind referred to above, which will have sufficient long-term stability under hydrolysis, especially in the biological environment of the eye.